Tetrahydrocannabinols are the active constituents of marihuana (hashish). They can be represented by the general chemical formula:
where R represents an alkyl chain of 3-10 carbon atoms, most commonly C5, and the dotted line represents optional unsaturation, including aromatic rings. The Δ1-3,4-trans-isomer, also referred to as Δ9-THC or dronabinol and having the chemical formula:
is the only active major constituent in hashish. It is physiologically active, and finds pharmaceutical use as an anti-emetic, e.g. for enhancing the appetite in patients suffering the side effects of chemotherapy, suffering from AIDS or anorexia. Other active homologs which have been reported are Δ8-THC, of formula:
reported to be present in marihuana at about one-tenth of the amount of Δ9-THC, and a compound of the formula of Δ9-THC but in which the pentyl substituent group is replaced by a propyl group, and identified in Pakistani hashish.
Active tetrahydrocannabinols are found in only very small quantities in the natural plant extracts. Moreover, they are found in admixture with a significant number of chemical isomers, from which it is very difficult to separate and purify the active compound(s). This is so also with synthetic THCs—synthetic processes for the most part produce mixtures of isomers. The separation and purification process is complicated by the fact that THCs are oils by nature, largely on account of the presence in the molecular structure of the alkyl group.